The present invention relates generally to synthetic resins and in particular to fluorinated epoxy resins.
The terminology pertaining to epoxy resins is varied. The term "epoxy" refers to the small ring grouping ##STR1## "Resin" refers to a number of physical properties of a material generally related to amorphous, sticky, soft, semifluid. Often an epoxy resin is prepared by co-polymerizing an epoxy monomer with another monomer termed a "curing agent." Hence the term "epoxy resin" may be used to designate the epoxy component only, the epoxy-curing agent mixture before reaction, or the final polymer that results from the reaction. The term "fluorinated epoxy resin" does not mean that any of the components are actually reacted with fluorine or fluorinating agents except at the early precursor stages, but simply means the product resulting from the reaction of fluorinated materials. The term "catalyst" is used in the conventional sense, i.e., a material present in a small amount which alters the speed of reaction.
Highly fluorinated epoxy resins, on account of their superior strength, stability, and low surface energy, are extremely important today and are becoming even more important with the increasing need for paints, coatings, adhesives, and structures for harsh environments. Difficulties in the manufacture and use of these compounds, especially the resins prepared from highly fluorinated diglycidyl ethers, are caused by the known curing agents. The curing agents used in synthesizing epoxy resins are usually dianhydrides, e.g., pyromellitic dianhydride and amines, e.g. dimethylaminoethane. The defects associated with dianhydride curing agents are high melting points, e.g., the melting point of pyromellitic dianhydride is 286.degree. C., very unaggressive reaction behavior with these epoxies, and a reduction of the fluorine content of the resin in comparison with the fluorinated epoxy monomer. While the amine curing agents react more readily, these compounds are not better in regards to the other two defects and these compounds are also objectionable due to the lower thermal stability and coloring of the resulting resins. The coloring is especially objectionable for resins which are used to fabricate sight glass tubes for boilers and evaporators and other types of windows. Fluorinated amines give some improvement. However these curing agents have several disadvantages which include poor long-term chemical stability, unaggressive reaction behavior with respect to epoxies, and excessive cost factors. Attempts, until now, to prepare fluorinated anhydride curing agents have been unsuccessful.